Chinese investor says he backed XIO Group big-time; it says he didn’t, and now he has filed suit

When Chinese billionaire Xie Zhikun toured Europe in the summer of 2015, his hosts took him to the Aston Martin factory in the English Midlands, to the women’s tennis final at Wimbledon and to dinner at London’s Connaught Hotel, where he was presented with a portrait of himself painted in tea, according to people who helped organize the visit.

Mr. Xie and his chaperones on the trip, executives at London private-equity firm XIO Group, stopped in on companies the firm was buying, according to current and former employees of...